EXPERIMENTAL AND NUMERICAL STUDY OF A TURBULENT AXISYMMETRIC JET IMPINGING ONTO A CIRCULAR CYLINDER IN OFFSET AND NON-OFFSET SITUATIONS

Abstract- In this study, an experimental and numerical analysis is done to study the flow characteristics of an offset and non-offset axisymmetric jet impingement on a circular cylinder. The purpose of this study is investigation of the behavior of the cutting gas jets and finding the optimum distance between nozzle and cylinder to achieve maximum cutting performance. Finite volume approach is used to solve the governing equations for a turbulent, incompressible jet numerically. According to the literatme the suitable turbulence model for this purpose is realizable k-e. Velocity and pressure fields around the cylinder and pressure and shear stress distribution on the cylinder surface are determined for various cases. Also, some experiments are done to validate repeatability of experiments and numerical results. Comparisons between numerical results and experimental measurements validate the accuracy of numerical results. Also, results show that if the horizontal distance between the nozzle outlet and the stagnation point of cylinder is 2.5D, the shear stress on the cylinder surface has maximum value. Therefore in this situation jet has a maximum performance in cutting procedure. Figure 3 shows the comparison between dimensionless shear stresses on the cylinder for different offsets. The results show that in all cases shear stresses are less than shear stresses in non-offset case except for offset = 0.4R. The reason of this phenomenon is the effect of wake and reversal flow. Applying offset to the jet moves the separation point to the back of the cylinder. Therefore, applying offset to the jet increases the region of the cylinder surface which is affected by the cutting procedure. Only a small region around θ = 180° is not affected by jet. This region can be cleaned by applying an inclined nozzle. Figures 4, 5 and 6 compare the numerical results with experimental measurements for static pressure on the cylinder perimeter for non-offset jet, offset = 0.4R, and offset = R, respectively. These figures show good agreement between experimental measurements and numerical results and validate the accuracy of numerical results.